1. Field of the Invention
This invention generally relates to apparatus of the type wherein signal information is recorded in parallel skewed tracks on a record medium and has particular application to a video tape recorder (VTR) in which stop-motion, slow-motion or fast-motion pictures as well as normal-motion pictures can be reproduced.
2. Description of the Prior Art
In a conventional VTR, a rotary transducer or head assembly is provided with one or more magnetic transducers which scan successive parallel tracks on a magnetic record tape so as to record and/or reproduce video signals in such tracks. In general, while the one or more transducers rotate so as to scan across the tape, the tape itself is transported longitudinally. A typical so-called helical scan VTR preferably includes two record and/or playback transducers mounted approximately 180.degree. apart on a suitable rotary assembly so as to alternately scan a magnetic tape which is helically wrapped about at least a portion of a guide drum forming a part of the transducer assembly. During recording, a tracking servo system controls the rotation of the transducers with respect to the tape movement, and control pulse signals are recorded on a marginal portion of the tape. During normal reproduction, the same or a similar servo control system is used to synchronize the movement of the tape to the rotation of the transducers in accordance with the recorded control pulse signals. Consequently, an accurate video picture can be displayed in response to the reproduced video signal. This accuracy is, in large part, due to the fact that the servo control system tends to control the relative movements and positions of the rotary transducers and the tape so that each transducer scans substantially the same track during a reproducing or playback operation as was scanned by it during the recording operation. Therefore, during normal reproducing, that is, playback at the normal tape speed, the servo system substantially serves to insure that the scanning path of each of the heads or transducers coincides with one of the previously recorded tracks. In one type of helical scan VTR, the adjacent parallel record tracks which are recorded by the alternate passes or scans of the magnetic heads or transducers are spaced apart from each other by guard bands. In another type of helical scan VTR, the recording density is increased by eliminating such guard bands and recording the parallel record tracks in abutting or substantially contiguous relation.
In existing helical scan VTRs wherein contiguous record tracks are recorded, the problem of crosstalk interference due to unwanted signals which are picked up from adjacent record tracks during a reproducing operation is avoided, at least in respect to high frequency signal components, by recording the adjacent record tracks with magnetic heads having respective gaps with different azimuth angles. As is known, if the luminance signal of a composite color video signal is frequency-modulated onto a relatively higher frequency carrier, then, because of the phenomenon of azimuth loss which is directly related to the frequency of the signals, those signals which are recorded in an adjacent track by a magnetic head having a different azimuth angle than the head which is used to reproduce the recorded signals from a given track will be substantially attenuated. Of course, the magnetic head used for reproducing signals recorded in each track should have the same azimuth angle as the head which was used to record the signals in that track.
However, it is bothersome and costly to provide the rotary transducer assembly of a VTR with heads having different azimuth angles and further to precisely position such heads relative to the supporting structures therefor so that the desired coincidence of the azimuth angles of heads used for recording and reproducing signals in particular tracks will be achieved even when the recording and reproducing operations are performed with different VTRs.
Recently, VTRs have been provided which are capable of various kinds of reproducing operations, such as "stop or still-motion", "slow-motion" and "quick or fast-motion". In these various reproducing modes, the tape speed differs from the speed during recording. Consequently, the scanning path of each head or transducer is different from the recorded track during these different reproducing modes, that is, the scanning path is inclined, or angularly disposed, with respect to the recorded track. This means that, in the various reproducing modes other than the "normal mode", guard band noise or crosstalk will result from the tracking errors or inclination of the scanning paths of the heads relative to the recorded tracks.
It has been proposed, for example, in U.S. Pat. No. 4,080,636, that such tracking errors in the scanning path of each rotary head or transducer can be corrected if each transducer is supported by an adjustable support assembly, such as, a so-called bi-morph leaf, which is adapted to deflect or flex in a direction, and by an amount depending upon the polarity and amplitude of an electrical drive signal applied thereacross. Hence, and as described in the aforementioned patent, the drive signal applied to the bi-morph leaf can be suitably controlled so as to deflect the transducer supported thereby in a direction transversely of the plane of rotation of the head or transducer and thereby cause its scanning path to coincide with the parallel record tracks which are scanned thereby. Although tracking errors are minimized or avoided by use of a suitably controlled bi-morph leaf, as aforesaid, it can be appreciated that deflection of the transducer or head in the direction transverse or perpendicular to its plane of rotation does not alter the azimuth angle of the head gap relative to the track being scanned. Thus, if the tracking error or deviation of the scanning path from a recorded track is accompanied by a difference between the actual azimuth angle of the scanning transducer or head from the azimuth angle with which the scanned track was recorded, the resulting azimuth loss or attenuation of the reproduced signal will not be substantially helped by the bi-morph leaf induced deflection of the head perpendicular to its plane of rotation.
Moreover, if a helical scan VTR having two diametrically opposed heads with different azimuth angles for minimizing crosstalk interference, as described above, is used in a "slow-motion" reproducing operation in which, for example, the tape is longitudinally driven or advanced at a speed which is one-half or one-quarter the tape speed during recording, each recorded track is scanned twice or four times, respectively, and, therefore, half of such repeated scans of each track may be effected with a head having an azimuth angle different from that of the head with which the scanned track was recorded. Accordingly, in the slow-motion reproducing mode, there may be substantial attenuation of the reproduced signal during at least some of the repetitive scans of each track.